In the operation of a well, there are any number of processes which may act to reduce production from the well. Initial drilling processes can create significant amounts of debris, including rock particulates, rock dust and oil mist. In addition, drilling muds and fluids may contain chemicals which can reduce the ability of the formation to produce fluids by reacting with the formation and/or formation fluids to produce precipitates and/or scale. Furthermore, some fluids may also cause clays within the formation to swell, further blocking the formation's ability to flow. The use of fluid loss control fluids may result in filter cake invading the near wellbore area, which could also decrease the formation near wellbore permeability. Over time, additional processes may act to allow water to imbibe into the formation, and/or asphaltenes and paraffins may deposit in the near wellbore area. Any one of these processes may act to decrease near wellbore permeability and production.
While wells may generally be drilled vertically, in some applications, it may be desirable to steer the wellbore away from vertical, or a wellbore may unintentionally deviate from vertical. It is possible to drill a well in which one or more portions of the wellbore travel horizontally or even such that they are angled up towards the surface. These wells with at least partially non-vertical wellbores are known as deviated or horizontal wells, and are frequently employed with formations which have low natural pressure as this technique increases wellbore exposure to the hydrocarbon-bearing formation. It is also possible to create multiple wellbore segments extending off a main horizontal wellbore. These multiple segments may comprise lateral segments or may form a fishbone-like structure. Furthermore, a vacuum may be employed where the formation pressure is insufficient for economic production. Regardless of the physical characteristics of the well, when the formation pressure or natural driving force is low, wells are particularly susceptible to the problems associated with deposits, rock dust/drilling fluids becoming impacted on the rock face, and/or imbibed water.
Furthermore, degradation may occur regardless of the manner in which the well is completed. Depending on the formation being drilled into and other factors known in the art, it may be desirable to insert a casing into the wellbore. In situations where casing is inserted into the entire wellbore, the well is known as a cased well. In contrast, if no casing is used, the well is known as an open hole well; and, if only a portion of the wellbore is cased, the well may be known as a partially cased hole or partially open hole. When pipe is run into an open hole section and not cemented in place it is called a liner and the well an open hole completion with liner. In some instances the liner may later be pulled or removed for various reasons. Again, regardless of whether a casing or liner is used, one or more of the previously described processes may act to reduce production.
For some wells, it may be desirable to increase formation flow by fracturing the fluid or gas bearing formation. One fracturing method involves the introduction of a fracturing fluid into the formation at high pressure such that cracks in the rock or fractures within the formation are caused to form. These fractures may be effective in increasing the permeability of the formation, and may bypass wellbore damage such as skin damage in the near wellbore area. In some instances a proppant such as natural sand, or engineered products such as coated sand or sintered bauxite may be used. The proppant may be mixed with the fracturing fluid so that following injection of the fracturing fluid, the proppant may be left in the created fractures, holding them open so that permeability is not lost. However, the use of fracturing fluid itself may adversely affect production as the fluid may act to block pores in the formation.
In yet other wells, it may be desirable to increase the surface area of the wellbore, as this may provide additional paths for fluid or gas to migrate from the formation to the wellbore. This additional surface area may be created by forming slots or other contours in the surface of the wellbore. However, again, care must be taken to ensure that in the process of creating the slots, additional debris is not introduced such that it could act to block the formation and hinder production.
Thus, there still remains a need for methods and compositions for cleaning wellbore and near-wellbore areas from damage related to drilling, work over operations and natural degradation of the wellbore from production, especially in low pressure formations. There is an additional need to perform cleaning in a manner such that an operator may precisely control the location of the cleaning. There is also a need for methods and apparatus suitable for cleaning a wellbore casing. Furthermore, there is a need for methods, apparatus and compositions used in the slotting and fracturing of a formation which leave substantially clean slots and/or fractures in the wellbore and near wellbore areas.